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Dandelion Seeds Fly Using ‘Impossible’ Method Never Before Seen in Nature

395 points by bcOpus 8y ago

miduil 8y ago
I find this extremely fascinating, I've never put any efforts into thinking how this is flying - just because it felt so natural and obvious. A great example of that the obvious can hide greater details we still haven't uncovered.
aidos 8y ago
That was a lovely little diversion! There’s a brief 1 minute clip in the article that’s worth watching. I do have one question though, how is the air flowing up through? It the seed not falling for that to happen?
- lordnacho 8y ago
  Yes, the seed is falling, but the vortex slows the fall enough for it to be useful in distributing the seed as far as possible.
  - ehnto 8y ago
    Some seeds have a small leaf attached, making them spin as they fall and slowing their descent for the same purpose. It's not about flying, just about prolonging the time spent in a moving body of air.
    - pouetpouet 8y ago
      Sycamore and linden are the perfect example of this.
  - 2_listerine_pls 8y ago
    My intuitive understanding is that the vortex is a consequence of the slower flow through and not the other way around.
    - salty_biscuits 8y ago
      Potential energy from gravity goes to kinetic energy of stable vortex ring rather than kinetic energy of falling down.
- snowwrestler 8y ago
  Wind can create upward movements of air near the ground.
- mhandley 8y ago
  It flys in the same way a glider flys. A glider generates lift over the wings, but the lift comes from the airflow, and you get the airflow by trading potential energy for kinetic energy. Thus the glider is always descending through the airmass, albeit at a very shallow glide angle. But the airmass itself isn't stationary - the sun heats the ground unevenly, so some air above it is warmer and rises, and some parts are colder and sink, with winds circulating between them. A glider can stay airborne for hours if the pilot is good at finding rising air, and circling within it. So long as the air is rising faster than the glider is descending within the airmass, the glider will gain altitude. The dandelion is doing the same thing. It's creating lift by descending slowly within the airmass, though the process of creating lift is via the vortex ring, rather than airflow over wings. Its aim is to fall very very slowly. Then it will often be falling slower than the airmass is rising, and it will be carried up and far away. Of course there's no pilot, so it can't actively seek out rising air, but there are an awful lot of dandelion seeds, and only a few need to get lucky to spread a long way.
- TeMPOraL 8y ago
  I imagine they get blown with the wind, start falling, which triggers the formation of the vortex - and that vortex is somewhat self-sustaining, almost completely arresting the fall.
dwighttk 8y ago
I missed where they described how this was "Impossible"
- macintux 8y ago
  "Researchers thought that an unattached vortex would be too unstable to persist in nature."
  - dwighttk 8y ago
    thanks
- ASalazarMX 8y ago
  Well, obviously not literally impossible, more like incredible. They float away because they form an unattached air vortex above themselves, and it sucks them up. Flight without work.
- dang 8y ago
  "Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize." https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
- PhasmaFelis 8y ago
  "Dandelion seeds fly using a method that researchers thought couldn’t work in the real world [...] Researchers thought that an unattached vortex would be too unstable to persist in nature."
apo 8y ago
Amazing that: (1) the mechanism involves a detached vortex; and (b) that it's taken millennia to understand what makes dandelion seeds fly.
- booleandilemma 8y ago
  Relevant xkcd: https://xkcd.com/1867/ https://xkcd.com/1867/
- pbhjpbhj 8y ago
  Re (b) they appear to "fly" just like any other small piece of stuff, just moving with the air, so I imagine it's more "there doesn't appear to be any need to explain it". They, dandelion seeds, appear to fly like other cotton-y plants do (eg heather [1]). I wonder if they creates these vortices too? I'd guess not as their structures aren't regular and they don't have the weighted 'drop' to give stability? [1] https://oregonstate.edu/dept/nursery-weeds/email_pubs/thistles/thistles.html https://oregonstate.edu/dept/nursery-weeds/email_pubs/thistl...
tines 8y ago
> Those structures act like the wings of a bird or aeroplane, generating pressure differences above and below the wing to fly. I thought we had settled this, airplane wings work by deflecting air downward, not by the Bernoulli effect, right?
- wahern 8y ago
  They're different ways to describe the same phenomenon. "[B]oth 'Bernoulli' and 'Newton' are correct." https://www.grc.nasa.gov/www/k-12/airplane/bernnew.html https://www.grc.nasa.gov/www/k-12/airplane/bernnew.html
  - captain_perl 8y ago
    > They're different ways to describe the same phenomenon. Well ... they're actually different ways to incorrectly describe the same phenomenon. Wind tunnels are still used for aircraft design because we can't accurately model aerodynamics.
    - dj-wonk 8y ago
      Please clarify what you mean by ‘accurately’ ... without reducing this discussion to a coarse dichotomy between ‘accurate’ or ‘not accurate’ —- which would miss a main point of what models do and why they are useful. My very rough understanding is that computer simulations of air flow are sufficently accurate for a high percentage of predictions for many kinds of objects. Fair? If not, under what cases does their accuracy suffer? Do we know why? I am interested in why wind tunnels are sometimes used. Possible reasons I see are: 1. building computer models of an object being tested is sufficently difficult that it is more efficient to test in a wind tunnel 2. computer simulations lose significant accuracy when it comes to certain conditions ... but I don’t know what these conditions are 3. human or policy issues, e.g. some people trust a wind tunnel result more than a computer simulation.
      - btrettel 8y ago
        Fluid dynamicist here. Short version: Scale models (like wind tunnels) are useful because the most accurate simulations are extremely computationally expensive or computationally intractable, and the faster less accurate simulations are often so inaccurate that they are untrustworthy. Scale models are not 100% trustworthy themselves, and to construct and use them you need to understand similarity theory. Long version: The general field is called computational fluid dynamics (CFD for short). There are broadly two types of turbulent computer simulations of flows: DNS and not-DNS. DNS stands for direct numerical simulation. These simulations are very accurate, and sometimes are regarded as more trustworthy than experiments because in a particular experiment you may not be able to set a variable precisely, but you can always set variables precisely in a simulation. Howver, in DNS you need to resolve all scales of the flow. Often this includes the "Kolmogorov scale" where turbulent dissipation occurs. It could also include even smaller scales like those involved in multiphase flows or combustion. This is so extremely computationally expensive that it's impractical (in terms of something you could run on a daily basis and iterate on) for anything but toy problems like "homogeneous isotropic turbulence". In terms of real world problems, DNS is limited to fairly simple geometries like pipe flows. Those simulations will take weeks on the most powerful supercomputers today. It's very rare for someone to attempt a DNS of a flow with a more complex geometry, and I'd argue that such works are mostly a waste of resources. Here's an interesting perspective on that: https://wjrider.wordpress.com/2015/12/25/the-unfortunate-myth-of-the-hero-calculation/ https://wjrider.wordpress.com/2015/12/25/the-unfortunate-myt... "Not-DNS" includes a variety of "turbulence modeling" approaches which basically try to reduce the computational cost to something more manageable. This can reduce the cost to hours or days on a single computer or cluster. The two most popular turbulence modeling approaches are called RANS and LES. Instead of solving the Navier-Stokes equations as is done in DNS, modified versions of the Navier-Stokes equations are solved. If you time average the equations instead, you'll get the Reynolds averaged Navier-Stokes (RANS) equations: https://en.wikipedia.org/wiki/Reynolds-averaged_Navier%E2%80%93Stokes_equations https://en.wikipedia.org/wiki/Reynolds-averaged_Navier%E2%80... These equations are "unclosed" in the sense that they contain more unknowns than equations. In principle, you could write a new equation for the unclosed term (which is called the Reynolds stress in the RANS equations), but you'll end up with even more unclosed terms. So, the unclosed terms are instead modeled. RANS is older, computationally cheaper, and usually computes the quantity that you want (e.g., a time averaged quantity). LES is newer, and has better justification in theory (e.g., good LES models converge to DNS if you make the grid finer, but RANS will not), but it often doesn't compute precisely what you want and the specifics of the LES models are often specified in inconsistent ways. My experience is that people tend to ignore the problems with LES or be ignorant of them. (Though I do believe LES is more trustworthy.) The problem is that modeling turbulence has proved to be rather difficult, and none of these models work particularly well. Some are better than others, but the more accurate ones typically are more computationally expensive. Personally, I don't trust any turbulence model outside of its calibration data. Some people lately have proposed that machine learning could construct a particularly accurate turbulence model, but that seems unlikely to me. People said that same things about chaos theory and other buzzwords in the past, but we're still waiting. Many turbulence models are fitted to a lot of data, and they're still not particularly credible. Also, machine learning doesn't take into account the governing equations. Methods which are similar to machine learning but do take into account the governing equations are typically called "model order reduction". If you want to do machine learning for turbulence, you actually should do model order reduction for turbulence. Otherwise, you're missing a big source of data: the governing equations themselves. (I could write more on this topic, in particular about constraints you'd want the model to fit which machine learning doesn't necessarily satisfy.) Anyhow, scale models are basically treating the world as a computer. Often testing at full scale is too expensive, particularly if you want to iterate. "Similarity theory" gives a theoretical basis to scale models, so that you know how to convert between the model and reality. One of the most important results in similarity theory is the Buckingham Pi Theorem: https://en.wikipedia.org/wiki/Buckingham_%CF%80_theorem https://en.wikipedia.org/wiki/Buckingham_%CF%80_theorem This theorem shows that two systems governed by the same physics are "similar" if they have the same dimensionless variables, even if the physical variables differ greatly. If any of this is confusing, I'd be happy to answer further questions.
pugworthy 8y ago
Something something "Bumblebees shouldn't be able to fly" something something. How is it we are shocked to find out we are sometimes wrong and not shocked that sometimes we get it right? My critique by the way is the headline, not the actual research. The headline is clickbait IMO, and just as I suppose some don't like my comment (not well thought out, emotional, etc.), the headline is the same. E.g., consider, "Curious unexpected aerodynamic principles of dandelion seeds lead scientists to new areas of discovery"
- repiret 8y ago
  I agree its a bad headline. Maybe "Dandelion Seeds Fly Using Method Not Previously Described in Nature", because: 1. Of course its been _observed_ before. As the video points out, just about every kid has observed it. The claim is really that nobody has previously understood the physics of it. 2. There's nothing impossible about it, clearly. Moreover, the article doesn't claim that people had previously analyzed the seeds behavior and came to the conclusion that it defies physics.
  - the8472 8y ago
    The vortex may not have been observed since air is mostly transparent.
    - whoopdedo 8y ago
      Or that no one had been able to answer, "What makes dandelion seeds fly?" because no one had asked the question before. At least not asked it in a way that prompted someone to look at a floating dandelion seed close enough to notice the vortex.
- amelius 8y ago
  > E.g., consider, "Curious unexpected aerodynamic principles of dandelion seeds lead scientists to new areas of discovery" You can even shorten that to "unexpected aerodynamic principles of dandelion seeds".
- Flowsion 8y ago
notatcomputer68 8y ago
I always thought dandelion seeds were so open to reduce weight while still catching a decent amount of the wind in its cross section, approximating the flight of a dust particle. Makes me wonder how much more of the wind a dandelion seed can catch with a vortex compared to if it didn't form one.
sova 8y ago
Does anybody have a link to a video of the lasers creating small vortices just above the dandelion surface?
- anigbrowl 8y ago
  Click through to the paper and you can view the figures and supplementary information for free. Protip: while it's frustrating to find a paywalled paper if you just want to know how it works the supplementary materials are usually unrestricted, better written, and easier to understand than the paper itself.
  - sova 8y ago
    Thanks ! That is a good pro tip. Did not think about supplemental papers and resources.
- JoshMandel 8y ago
  https://static-content.springer.com/esm/art%3A10.1038%2Fs41586-018-0604-2/MediaObjects/41586_2018_604_MOESM4_ESM.mp4 https://static-content.springer.com/esm/art%3A10.1038%2Fs415... https://static-content.springer.com/esm/art%3A10.1038%2Fs41586-018-0604-2/MediaObjects/41586_2018_604_MOESM5_ESM.mp4 https://static-content.springer.com/esm/art%3A10.1038%2Fs415... https://static-content.springer.com/esm/art%3A10.1038%2Fs41586-018-0604-2/MediaObjects/41586_2018_604_MOESM6_ESM.mp4 https://static-content.springer.com/esm/art%3A10.1038%2Fs415... https://static-content.springer.com/esm/art%3A10.1038%2Fs41586-018-0604-2/MediaObjects/41586_2018_604_MOESM7_ESM.mp4 https://static-content.springer.com/esm/art%3A10.1038%2Fs415... https://static-content.springer.com/esm/art%3A10.1038%2Fs41586-018-0604-2/MediaObjects/41586_2018_604_MOESM8_ESM.mp4 https://static-content.springer.com/esm/art%3A10.1038%2Fs415...
  - chrisweekly 8y ago
    Thank you. That first video is just mesmerizing.
mattdemon 8y ago
Wow, new parachute designs may be possible then! They will look scary, but can be more effective.
- saudioger 8y ago
  Ehhh, I imagine the seed/filament weight ratio is much closer than the human/filament weight ratio... if you blow this up to human size/weight proportions the filaments would likely need to be gigantic.
  - marcosdumay 8y ago
    I don't think you can scale the filaments up. Scaling this up would mean adding small holes to a parachute and filaments around those... And then we would get into the task of folding something full of small filaments.
- namirez 8y ago
  Probably not! This phenomenon is not scale-independent. There is a parameter called the Reynolds number (Re for short) which is the ratio of intertial forces to viscous forces. For a dandelion seed Re is small which is the key to the stability of the vortex. For a parachute, the Re number is much higher which makes the dynamics of the flow chaotic (called turbulence). There is a critical Re number beyond which There is no way keep the vortex stable, or as they call it, the vortex bursts.
  - btrettel 8y ago
    You're most likely right, but there is at least one caveat which might be able to help if we're lucky. (I'm a fluid dynamicist, though not an aerodynamicist.) The Reynolds number is only part of the picture. You also need a measure of the strength of the turbulence. A common measure is the "turbulence intensity", which you can think of as the standard deviation of the velocity divided by the mean of the velocity. (Though that's only exactly true in "isotropic turbulence".) In certain circumstances you can compensate for a higher Reynolds number with a lower turbulence intensity. The bristles of the dandelion may have a turbulence reduction ability, so perhaps this is already being done. I'm not certain how to reduce the turbulence level further as in this case it's mostly an ambient property which is beyond the control of the dandelion. Some sort of honeycomb structure upstream of the bristles might help, or it might hurt; it depends on the details. Here are some examples: Pipe flow can remain laminar for higher Reynolds numbers if the turbulence intensity is low enough. Though special turbulence control approaches (e.g., eliminating vibrations which could trigger transition to turbulence) laminar pipe flows have been observed at a Reynolds numbers of about 100000, about 50 times higher than the typical Reynolds number where laminar flow ends. Here's a quote from a review article: https://www.annualreviews.org/doi/abs/10.1146/annurev-fluid-122109-160652 https://www.annualreviews.org/doi/abs/10.1146/annurev-fluid-... > The impression gained from presenting data in this way is that there is a transition between two definable states. One is the relatively rare but well-defined state of motion, laminar flow, and the other is the more common and ill-defined state of turbulence. Experimental evidence suggests that the laminar state can be achieved in pipe flows over a wide range of Re with the record standing at Re = 100,000 by Pfenniger (1961). Reynolds himself managed to achieve Re = 13,000, and Ekman (1911) later improved on this to ∼50,000 using Reynolds’ original apparatus. [...] Achieving laminar flows at high values of Re is an indication of the quality of an experimental facility and gives some confidence that the observations will not be contaminated by extraneous background disturbances such as entrance flow effects, convection, and geometrical irregularities. Matching the turbulence intensity of two wind tunnels is often necessary to make the results comparable between the two wind tunnels. In the first volume of Sidney Goldstein's "Modern Developments in Fluid Dynamics", there's a plot showing (if I recall correctly) the Reynolds number at which the "drag crisis" occurs as a function of turbulence intensity. This basically means that the drag coefficient can be very sensitive to the turbulence intensity, at least in special circumstances. (Why I wrote this: In my dissertation, I have an entire section about how turbulence intensity is too frequently neglected in analyses, particularly for the problem I'm studying for my PhD.)
holografix 8y ago
Could we design better parachutes using this tech?
namirez 8y ago
Fascinating! For what it's worth, detached vortices are also critical to the takeoff and landing of airplanes with delta wings, such as the Concorde.
jahbrewski 8y ago
Is there a link to the actual journal article?
- JoshMandel 8y ago
  https://www.nature.com/articles/s41586-018-0604-2 https://www.nature.com/articles/s41586-018-0604-2
- dpfu 8y ago
  There is, right in the article: Cummins, C. et al. Nature https://doi.org/10.1038/s41586-018-0604-2 https://doi.org/10.1038/s41586-018-0604-2 (2018).
mindfulhack 8y ago
It's like nature's had millions of years to crunch through its own AI / machine learning of evolution and adaptation, and we're about to unleash the same thing on an impossibly faster scale. Imagine the technological breakthroughs that are going to happen. I'm optimistic.
- bromuro 8y ago
  Are we re-discovering nature as a big not-artificial intelligence? like that big entity someone will start to respect, venerate and serve as a mythical goddess?
  - sixstringtheory 8y ago
    A syncretization of technology and scientific thought, hearkening back to our more animistic tendencies, sounds both poetic and plausible.
    - creep 8y ago
      I don't think worship is an "animistic" quality. I think the tendency to worship is very much a refined trait in highly intelligent organisms.
      - onion2k 8y ago
        You're right in the sense that ritualised, repeated behaviour performed for no obvious gain is something very unusual. Most animals don't waste energy on things that don't have a material impact on their life. I'd disagree with your point about intelligence though. It's simply that we have more resources than we need. Even the stupidest animals would develop rituals if they could afford to.
        mafm 8y ago
        Animals like rats and pigeons actually do develop superstitious rituals. Skinner documented it in 1948, and there's a fair bit of literature on it. https://psychclassics.yorku.ca/Skinner/Pigeon/ https://psychclassics.yorku.ca/Skinner/Pigeon/
strainer 8y ago
""" """ "" ^v^ "" "" ^v^ "" "" ^v^ "" ... low pressure """...""" held by vortex ######### ### dandelion falling """"""""" """ rising air I wonder about the chances of creating this kind of toroidal vortex above a duct for lift. It seems necessary for the air to pass in the same direction as the lift, yet lift is normally created by throwing air in the opposite direction.
- dleslie 8y ago
  Excuse me, I'm going to go launch SyncTerm now and browse some Mystic and SynchroNet boards.
  - deleted 8y ago
    [deleted]
  - Angostura 8y ago
    I'm going to dig through the alt.fan.warlord archives
- CraneWorm 8y ago
  I had to read your comment twice before I realized it's not, in fact, a short poem. [Edit] Maybe it is after all. :)
zepearl 8y ago
The result of natural/evolutionary selection? Would be interesting to know if there are different types of dandelions (I mean the part used to "fly") used by the same type of seed, each type adapted/optimized for a particular climate (e.g. humid for asian areas, dry for african areas, windy for coastal areas, ...).
- deleted 8y ago
  [deleted]
- adaptiveValleys 8y ago
  The criteria for adaptive evolution, in the classical Darwinian sense, are: 1). Reproduction. 2). Variation between the products of reproduction. 3). Heritability between those variants. 4). Differential success among the variants. Anything that has those four characteristics will experience adaptive evolution. Where it gets really fascinating is when you realize it applies to things that don't go through biological reproduction, for example the graphical user interface.
  - zepearl 8y ago
    Well, about the GUI: I'm not sure that that's following the rules; most try to blindly follow trends, big companies tend to impose their GUIs, many implement anything which is low-effort (therefore already made available by 3rd parties), etc... => I don't see much selection/competitiveness here.
kakarot 8y ago
> Never Before Seen in Nature > Many insects harbour such filter-like structures on their wings or legs, suggesting that the use of detached vortices for flight or swimming might be relatively common I sense a bit of disconnect between the article and the headline.
- taneq 8y ago
  Also: > When some animals, aeroplanes or seeds fly, rings of circulating air called vortices form in contact with their wings or wing-like surfaces. > Researchers thought that an unattached vortex would be too unstable to persist in nature. I guess those animals and seeds aren't natural then?
  - mclehman 8y ago
    Aren't those two sections contrasting "in contact" with "unattached"?
    - taneq 8y ago
      Huh, looks like I misread that bit. Good catch!
  - kissickas 8y ago
    What makes a vortex unattached?
taneq 8y ago
This reminds me of the thing recently about spiders using electrostatic tension in the air to generate lift with a streamer of silk. Evolution is crazy good at finding and exploiting quirks in physics.
- ironic_ali 8y ago
  I was going to mention this as I worked a couple of summers picking cherries and every morning you'd be plowing through spider lines about head height between the trees. There were lots of theories that got worse after a few beers at the end of the work day, but it had puzzled me for a couple of decades. Then learnt about spiders using the electromagnetic energy fields to 'fly'. Nature is amazing.
paavoova 8y ago
Perhaps ignorance on my part, but: why do they require highspeed cameras and laser illumination to figure this out in 2018? Shouldn't physics by able to model such a relatively simply structure and how air would move through and around it?
- bcOpus 8y ago
  Fluid dynamics is hard and a simulation can only work with the inputs and parameters you set it up with.
- nosjwshere 8y ago
  reverse engineering is cheaper
- coldtea 8y ago
  "Relatively simply structures" can be nigh impossible to model... https://en.wikipedia.org/wiki/Three-body_problem https://en.wikipedia.org/wiki/Three-body_problem
cmurf 8y ago
They aren't just good at flying. They're good at traveling on shoes, and releasing on hikes, finding their way in national forests and wilderness where they'd otherwise have had zero chance ending up.
im3w1l 8y ago
If you find this interesting I highly recommend you to look at some vape-trick videos. Smoke/steam is great at visualizing vortices, and it's absolutely astonishing how much aerodynamically control some people can achieve. Creating lots of small vortices in rapid succession, merging vortices, splitting vortices, letting vortices "suck in" other vortices. https://www.youtube.com/watch?v=Tmv228G8R4o&time_continue=1m https://www.youtube.com/watch?v=Tmv228G8R4o&time_continue=1m
- hasahmed 8y ago
  I feel like I could have enjoyed that if those dudes weren't such giant fuck boys
  - dang 8y ago
    Please don't do this here.
seandavidfisher 8y ago
> Previous studies have found that dandelion seeds always have between 90 and 110 bristles, says Nakayama Those poor research assistants. Imagine counting hundreds of dandelion bristles every day. Probably still not possible with AI/image recognition either.
- deleted 8y ago
  [deleted]
- nl 8y ago
  That would 100% be possible with image recognition. Segment using UNet, then measure the remaining joined pixels. (Well thanks for the downvotes. I do this as my job, so I guess I'm doing the impossible or something)
  - mdda 8y ago
    Perhaps people are wondering how your UNet is going to see the bristles on the other side of the dandelion seed.
    - comex 8y ago
      Take photos from multiple angles?
      - TeMPOraL 8y ago
        Now you have a pretty ugly correspondence problem to solve.
        titzer 8y ago
        I'm glad we have experts who can count to 100 instead. /s
      - kabacha 8y ago
        And how do you deduplicate the ones that are visible on multiple angles?
a012 8y ago
I always thought dandelion seeds are like small parachutes those are slowly falling down.
mar77i 8y ago
Oh look, a vortex ring. Hermann von Helmholtz, while studying fluid dynamics predicted that vortex rings had to exist. https://www.youtube.com/watch?v=Bcr9-93wXng https://www.youtube.com/watch?v=Bcr9-93wXng
jhabdas 8y ago
Webpage not available The webpage at https://www.nature.com/articles/d41586-018-07084-8 https://www.nature.com/articles/d41586-018-07084-8 could not be loaded because: net::ERR_TOO_MANY_REDIRECTS

395 points by bcOpus 8y ago

I find this extremely fascinating, I've never put any efforts into thinking how this is flying - just because it felt so natural and obvious. A great example of that the obvious can hide greater details we still haven't uncovered.

aidos 8y ago

That was a lovely little diversion! There’s a brief 1 minute clip in the article that’s worth watching. I do have one question though, how is the air flowing up through? It the seed not falling for that to happen?

lordnacho 8y ago
Yes, the seed is falling, but the vortex slows the fall enough for it to be useful in distributing the seed as far as possible.
- ehnto 8y ago
  Some seeds have a small leaf attached, making them spin as they fall and slowing their descent for the same purpose. It's not about flying, just about prolonging the time spent in a moving body of air.
  - pouetpouet 8y ago
    Sycamore and linden are the perfect example of this.
- 2_listerine_pls 8y ago
  My intuitive understanding is that the vortex is a consequence of the slower flow through and not the other way around.
  - salty_biscuits 8y ago
    Potential energy from gravity goes to kinetic energy of stable vortex ring rather than kinetic energy of falling down.
snowwrestler 8y ago
Wind can create upward movements of air near the ground.
mhandley 8y ago
It flys in the same way a glider flys. A glider generates lift over the wings, but the lift comes from the airflow, and you get the airflow by trading potential energy for kinetic energy. Thus the glider is always descending through the airmass, albeit at a very shallow glide angle. But the airmass itself isn't stationary - the sun heats the ground unevenly, so some air above it is warmer and rises, and some parts are colder and sink, with winds circulating between them. A glider can stay airborne for hours if the pilot is good at finding rising air, and circling within it. So long as the air is rising faster than the glider is descending within the airmass, the glider will gain altitude. The dandelion is doing the same thing. It's creating lift by descending slowly within the airmass, though the process of creating lift is via the vortex ring, rather than airflow over wings. Its aim is to fall very very slowly. Then it will often be falling slower than the airmass is rising, and it will be carried up and far away. Of course there's no pilot, so it can't actively seek out rising air, but there are an awful lot of dandelion seeds, and only a few need to get lucky to spread a long way.
TeMPOraL 8y ago
I imagine they get blown with the wind, start falling, which triggers the formation of the vortex - and that vortex is somewhat self-sustaining, almost completely arresting the fall.

dwighttk 8y ago

I missed where they described how this was "Impossible"

macintux 8y ago
"Researchers thought that an unattached vortex would be too unstable to persist in nature."
- dwighttk 8y ago
  thanks
ASalazarMX 8y ago
Well, obviously not literally impossible, more like incredible. They float away because they form an unattached air vortex above themselves, and it sucks them up. Flight without work.
dang 8y ago
"Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize." https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
PhasmaFelis 8y ago
"Dandelion seeds fly using a method that researchers thought couldn’t work in the real world [...] Researchers thought that an unattached vortex would be too unstable to persist in nature."

apo 8y ago

Amazing that: (1) the mechanism involves a detached vortex; and (b) that it's taken millennia to understand what makes dandelion seeds fly.

booleandilemma 8y ago
Relevant xkcd: https://xkcd.com/1867/ https://xkcd.com/1867/
pbhjpbhj 8y ago
Re (b) they appear to "fly" just like any other small piece of stuff, just moving with the air, so I imagine it's more "there doesn't appear to be any need to explain it". They, dandelion seeds, appear to fly like other cotton-y plants do (eg heather [1]). I wonder if they creates these vortices too? I'd guess not as their structures aren't regular and they don't have the weighted 'drop' to give stability? [1] https://oregonstate.edu/dept/nursery-weeds/email_pubs/thistles/thistles.html https://oregonstate.edu/dept/nursery-weeds/email_pubs/thistl...

tines 8y ago

> Those structures act like the wings of a bird or aeroplane, generating pressure differences above and below the wing to fly. I thought we had settled this, airplane wings work by deflecting air downward, not by the Bernoulli effect, right?

wahern 8y ago
They're different ways to describe the same phenomenon. "[B]oth 'Bernoulli' and 'Newton' are correct." https://www.grc.nasa.gov/www/k-12/airplane/bernnew.html https://www.grc.nasa.gov/www/k-12/airplane/bernnew.html
- captain_perl 8y ago
  > They're different ways to describe the same phenomenon. Well ... they're actually different ways to incorrectly describe the same phenomenon. Wind tunnels are still used for aircraft design because we can't accurately model aerodynamics.
  - dj-wonk 8y ago
    Please clarify what you mean by ‘accurately’ ... without reducing this discussion to a coarse dichotomy between ‘accurate’ or ‘not accurate’ —- which would miss a main point of what models do and why they are useful. My very rough understanding is that computer simulations of air flow are sufficently accurate for a high percentage of predictions for many kinds of objects. Fair? If not, under what cases does their accuracy suffer? Do we know why? I am interested in why wind tunnels are sometimes used. Possible reasons I see are: 1. building computer models of an object being tested is sufficently difficult that it is more efficient to test in a wind tunnel 2. computer simulations lose significant accuracy when it comes to certain conditions ... but I don’t know what these conditions are 3. human or policy issues, e.g. some people trust a wind tunnel result more than a computer simulation.
    - btrettel 8y ago
      Fluid dynamicist here. Short version: Scale models (like wind tunnels) are useful because the most accurate simulations are extremely computationally expensive or computationally intractable, and the faster less accurate simulations are often so inaccurate that they are untrustworthy. Scale models are not 100% trustworthy themselves, and to construct and use them you need to understand similarity theory. Long version: The general field is called computational fluid dynamics (CFD for short). There are broadly two types of turbulent computer simulations of flows: DNS and not-DNS. DNS stands for direct numerical simulation. These simulations are very accurate, and sometimes are regarded as more trustworthy than experiments because in a particular experiment you may not be able to set a variable precisely, but you can always set variables precisely in a simulation. Howver, in DNS you need to resolve all scales of the flow. Often this includes the "Kolmogorov scale" where turbulent dissipation occurs. It could also include even smaller scales like those involved in multiphase flows or combustion. This is so extremely computationally expensive that it's impractical (in terms of something you could run on a daily basis and iterate on) for anything but toy problems like "homogeneous isotropic turbulence". In terms of real world problems, DNS is limited to fairly simple geometries like pipe flows. Those simulations will take weeks on the most powerful supercomputers today. It's very rare for someone to attempt a DNS of a flow with a more complex geometry, and I'd argue that such works are mostly a waste of resources. Here's an interesting perspective on that: https://wjrider.wordpress.com/2015/12/25/the-unfortunate-myth-of-the-hero-calculation/ https://wjrider.wordpress.com/2015/12/25/the-unfortunate-myt... "Not-DNS" includes a variety of "turbulence modeling" approaches which basically try to reduce the computational cost to something more manageable. This can reduce the cost to hours or days on a single computer or cluster. The two most popular turbulence modeling approaches are called RANS and LES. Instead of solving the Navier-Stokes equations as is done in DNS, modified versions of the Navier-Stokes equations are solved. If you time average the equations instead, you'll get the Reynolds averaged Navier-Stokes (RANS) equations: https://en.wikipedia.org/wiki/Reynolds-averaged_Navier%E2%80%93Stokes_equations https://en.wikipedia.org/wiki/Reynolds-averaged_Navier%E2%80... These equations are "unclosed" in the sense that they contain more unknowns than equations. In principle, you could write a new equation for the unclosed term (which is called the Reynolds stress in the RANS equations), but you'll end up with even more unclosed terms. So, the unclosed terms are instead modeled. RANS is older, computationally cheaper, and usually computes the quantity that you want (e.g., a time averaged quantity). LES is newer, and has better justification in theory (e.g., good LES models converge to DNS if you make the grid finer, but RANS will not), but it often doesn't compute precisely what you want and the specifics of the LES models are often specified in inconsistent ways. My experience is that people tend to ignore the problems with LES or be ignorant of them. (Though I do believe LES is more trustworthy.) The problem is that modeling turbulence has proved to be rather difficult, and none of these models work particularly well. Some are better than others, but the more accurate ones typically are more computationally expensive. Personally, I don't trust any turbulence model outside of its calibration data. Some people lately have proposed that machine learning could construct a particularly accurate turbulence model, but that seems unlikely to me. People said that same things about chaos theory and other buzzwords in the past, but we're still waiting. Many turbulence models are fitted to a lot of data, and they're still not particularly credible. Also, machine learning doesn't take into account the governing equations. Methods which are similar to machine learning but do take into account the governing equations are typically called "model order reduction". If you want to do machine learning for turbulence, you actually should do model order reduction for turbulence. Otherwise, you're missing a big source of data: the governing equations themselves. (I could write more on this topic, in particular about constraints you'd want the model to fit which machine learning doesn't necessarily satisfy.) Anyhow, scale models are basically treating the world as a computer. Often testing at full scale is too expensive, particularly if you want to iterate. "Similarity theory" gives a theoretical basis to scale models, so that you know how to convert between the model and reality. One of the most important results in similarity theory is the Buckingham Pi Theorem: https://en.wikipedia.org/wiki/Buckingham_%CF%80_theorem https://en.wikipedia.org/wiki/Buckingham_%CF%80_theorem This theorem shows that two systems governed by the same physics are "similar" if they have the same dimensionless variables, even if the physical variables differ greatly. If any of this is confusing, I'd be happy to answer further questions.

pugworthy 8y ago

Something something "Bumblebees shouldn't be able to fly" something something. How is it we are shocked to find out we are sometimes wrong and not shocked that sometimes we get it right? My critique by the way is the headline, not the actual research. The headline is clickbait IMO, and just as I suppose some don't like my comment (not well thought out, emotional, etc.), the headline is the same. E.g., consider, "Curious unexpected aerodynamic principles of dandelion seeds lead scientists to new areas of discovery"

repiret 8y ago
I agree its a bad headline. Maybe "Dandelion Seeds Fly Using Method Not Previously Described in Nature", because: 1. Of course its been _observed_ before. As the video points out, just about every kid has observed it. The claim is really that nobody has previously understood the physics of it. 2. There's nothing impossible about it, clearly. Moreover, the article doesn't claim that people had previously analyzed the seeds behavior and came to the conclusion that it defies physics.
- the8472 8y ago
  The vortex may not have been observed since air is mostly transparent.
  - whoopdedo 8y ago
    Or that no one had been able to answer, "What makes dandelion seeds fly?" because no one had asked the question before. At least not asked it in a way that prompted someone to look at a floating dandelion seed close enough to notice the vortex.
amelius 8y ago
> E.g., consider, "Curious unexpected aerodynamic principles of dandelion seeds lead scientists to new areas of discovery" You can even shorten that to "unexpected aerodynamic principles of dandelion seeds".
Flowsion 8y ago

notatcomputer68 8y ago

I always thought dandelion seeds were so open to reduce weight while still catching a decent amount of the wind in its cross section, approximating the flight of a dust particle. Makes me wonder how much more of the wind a dandelion seed can catch with a vortex compared to if it didn't form one.

sova 8y ago

Does anybody have a link to a video of the lasers creating small vortices just above the dandelion surface?

anigbrowl 8y ago
Click through to the paper and you can view the figures and supplementary information for free. Protip: while it's frustrating to find a paywalled paper if you just want to know how it works the supplementary materials are usually unrestricted, better written, and easier to understand than the paper itself.
- sova 8y ago
  Thanks ! That is a good pro tip. Did not think about supplemental papers and resources.
JoshMandel 8y ago
https://static-content.springer.com/esm/art%3A10.1038%2Fs41586-018-0604-2/MediaObjects/41586_2018_604_MOESM4_ESM.mp4 https://static-content.springer.com/esm/art%3A10.1038%2Fs415... https://static-content.springer.com/esm/art%3A10.1038%2Fs41586-018-0604-2/MediaObjects/41586_2018_604_MOESM5_ESM.mp4 https://static-content.springer.com/esm/art%3A10.1038%2Fs415... https://static-content.springer.com/esm/art%3A10.1038%2Fs41586-018-0604-2/MediaObjects/41586_2018_604_MOESM6_ESM.mp4 https://static-content.springer.com/esm/art%3A10.1038%2Fs415... https://static-content.springer.com/esm/art%3A10.1038%2Fs41586-018-0604-2/MediaObjects/41586_2018_604_MOESM7_ESM.mp4 https://static-content.springer.com/esm/art%3A10.1038%2Fs415... https://static-content.springer.com/esm/art%3A10.1038%2Fs41586-018-0604-2/MediaObjects/41586_2018_604_MOESM8_ESM.mp4 https://static-content.springer.com/esm/art%3A10.1038%2Fs415...
- chrisweekly 8y ago
  Thank you. That first video is just mesmerizing.

mattdemon 8y ago

Wow, new parachute designs may be possible then! They will look scary, but can be more effective.

saudioger 8y ago
Ehhh, I imagine the seed/filament weight ratio is much closer than the human/filament weight ratio... if you blow this up to human size/weight proportions the filaments would likely need to be gigantic.
- marcosdumay 8y ago
  I don't think you can scale the filaments up. Scaling this up would mean adding small holes to a parachute and filaments around those... And then we would get into the task of folding something full of small filaments.
namirez 8y ago
Probably not! This phenomenon is not scale-independent. There is a parameter called the Reynolds number (Re for short) which is the ratio of intertial forces to viscous forces. For a dandelion seed Re is small which is the key to the stability of the vortex. For a parachute, the Re number is much higher which makes the dynamics of the flow chaotic (called turbulence). There is a critical Re number beyond which There is no way keep the vortex stable, or as they call it, the vortex bursts.
- btrettel 8y ago
  You're most likely right, but there is at least one caveat which might be able to help if we're lucky. (I'm a fluid dynamicist, though not an aerodynamicist.) The Reynolds number is only part of the picture. You also need a measure of the strength of the turbulence. A common measure is the "turbulence intensity", which you can think of as the standard deviation of the velocity divided by the mean of the velocity. (Though that's only exactly true in "isotropic turbulence".) In certain circumstances you can compensate for a higher Reynolds number with a lower turbulence intensity. The bristles of the dandelion may have a turbulence reduction ability, so perhaps this is already being done. I'm not certain how to reduce the turbulence level further as in this case it's mostly an ambient property which is beyond the control of the dandelion. Some sort of honeycomb structure upstream of the bristles might help, or it might hurt; it depends on the details. Here are some examples: Pipe flow can remain laminar for higher Reynolds numbers if the turbulence intensity is low enough. Though special turbulence control approaches (e.g., eliminating vibrations which could trigger transition to turbulence) laminar pipe flows have been observed at a Reynolds numbers of about 100000, about 50 times higher than the typical Reynolds number where laminar flow ends. Here's a quote from a review article: https://www.annualreviews.org/doi/abs/10.1146/annurev-fluid-122109-160652 https://www.annualreviews.org/doi/abs/10.1146/annurev-fluid-... > The impression gained from presenting data in this way is that there is a transition between two definable states. One is the relatively rare but well-defined state of motion, laminar flow, and the other is the more common and ill-defined state of turbulence. Experimental evidence suggests that the laminar state can be achieved in pipe flows over a wide range of Re with the record standing at Re = 100,000 by Pfenniger (1961). Reynolds himself managed to achieve Re = 13,000, and Ekman (1911) later improved on this to ∼50,000 using Reynolds’ original apparatus. [...] Achieving laminar flows at high values of Re is an indication of the quality of an experimental facility and gives some confidence that the observations will not be contaminated by extraneous background disturbances such as entrance flow effects, convection, and geometrical irregularities. Matching the turbulence intensity of two wind tunnels is often necessary to make the results comparable between the two wind tunnels. In the first volume of Sidney Goldstein's "Modern Developments in Fluid Dynamics", there's a plot showing (if I recall correctly) the Reynolds number at which the "drag crisis" occurs as a function of turbulence intensity. This basically means that the drag coefficient can be very sensitive to the turbulence intensity, at least in special circumstances. (Why I wrote this: In my dissertation, I have an entire section about how turbulence intensity is too frequently neglected in analyses, particularly for the problem I'm studying for my PhD.)

holografix 8y ago

Could we design better parachutes using this tech?

namirez 8y ago

Fascinating! For what it's worth, detached vortices are also critical to the takeoff and landing of airplanes with delta wings, such as the Concorde.

jahbrewski 8y ago

Is there a link to the actual journal article?

JoshMandel 8y ago
https://www.nature.com/articles/s41586-018-0604-2 https://www.nature.com/articles/s41586-018-0604-2
dpfu 8y ago
There is, right in the article: Cummins, C. et al. Nature https://doi.org/10.1038/s41586-018-0604-2 https://doi.org/10.1038/s41586-018-0604-2 (2018).

mindfulhack 8y ago

It's like nature's had millions of years to crunch through its own AI / machine learning of evolution and adaptation, and we're about to unleash the same thing on an impossibly faster scale. Imagine the technological breakthroughs that are going to happen. I'm optimistic.

bromuro 8y ago
Are we re-discovering nature as a big not-artificial intelligence? like that big entity someone will start to respect, venerate and serve as a mythical goddess?
- sixstringtheory 8y ago
  A syncretization of technology and scientific thought, hearkening back to our more animistic tendencies, sounds both poetic and plausible.
  - creep 8y ago
    I don't think worship is an "animistic" quality. I think the tendency to worship is very much a refined trait in highly intelligent organisms.
    - onion2k 8y ago
      You're right in the sense that ritualised, repeated behaviour performed for no obvious gain is something very unusual. Most animals don't waste energy on things that don't have a material impact on their life. I'd disagree with your point about intelligence though. It's simply that we have more resources than we need. Even the stupidest animals would develop rituals if they could afford to.
      - mafm 8y ago
        Animals like rats and pigeons actually do develop superstitious rituals. Skinner documented it in 1948, and there's a fair bit of literature on it. https://psychclassics.yorku.ca/Skinner/Pigeon/ https://psychclassics.yorku.ca/Skinner/Pigeon/

strainer 8y ago

""" """ "" ^v^ "" "" ^v^ "" "" ^v^ "" ... low pressure """...""" held by vortex ######### ### dandelion falling """"""""" """ rising air I wonder about the chances of creating this kind of toroidal vortex above a duct for lift. It seems necessary for the air to pass in the same direction as the lift, yet lift is normally created by throwing air in the opposite direction.

dleslie 8y ago
Excuse me, I'm going to go launch SyncTerm now and browse some Mystic and SynchroNet boards.
- deleted 8y ago
  [deleted]
- Angostura 8y ago
  I'm going to dig through the alt.fan.warlord archives
CraneWorm 8y ago
I had to read your comment twice before I realized it's not, in fact, a short poem. [Edit] Maybe it is after all. :)

zepearl 8y ago

The result of natural/evolutionary selection? Would be interesting to know if there are different types of dandelions (I mean the part used to "fly") used by the same type of seed, each type adapted/optimized for a particular climate (e.g. humid for asian areas, dry for african areas, windy for coastal areas, ...).

deleted 8y ago
[deleted]
adaptiveValleys 8y ago
The criteria for adaptive evolution, in the classical Darwinian sense, are: 1). Reproduction. 2). Variation between the products of reproduction. 3). Heritability between those variants. 4). Differential success among the variants. Anything that has those four characteristics will experience adaptive evolution. Where it gets really fascinating is when you realize it applies to things that don't go through biological reproduction, for example the graphical user interface.
- zepearl 8y ago
  Well, about the GUI: I'm not sure that that's following the rules; most try to blindly follow trends, big companies tend to impose their GUIs, many implement anything which is low-effort (therefore already made available by 3rd parties), etc... => I don't see much selection/competitiveness here.

kakarot 8y ago

> Never Before Seen in Nature > Many insects harbour such filter-like structures on their wings or legs, suggesting that the use of detached vortices for flight or swimming might be relatively common I sense a bit of disconnect between the article and the headline.

taneq 8y ago
Also: > When some animals, aeroplanes or seeds fly, rings of circulating air called vortices form in contact with their wings or wing-like surfaces. > Researchers thought that an unattached vortex would be too unstable to persist in nature. I guess those animals and seeds aren't natural then?
- mclehman 8y ago
  Aren't those two sections contrasting "in contact" with "unattached"?
  - taneq 8y ago
    Huh, looks like I misread that bit. Good catch!
- kissickas 8y ago
  What makes a vortex unattached?

taneq 8y ago

This reminds me of the thing recently about spiders using electrostatic tension in the air to generate lift with a streamer of silk. Evolution is crazy good at finding and exploiting quirks in physics.

ironic_ali 8y ago
I was going to mention this as I worked a couple of summers picking cherries and every morning you'd be plowing through spider lines about head height between the trees. There were lots of theories that got worse after a few beers at the end of the work day, but it had puzzled me for a couple of decades. Then learnt about spiders using the electromagnetic energy fields to 'fly'. Nature is amazing.

paavoova 8y ago

Perhaps ignorance on my part, but: why do they require highspeed cameras and laser illumination to figure this out in 2018? Shouldn't physics by able to model such a relatively simply structure and how air would move through and around it?

bcOpus 8y ago
Fluid dynamics is hard and a simulation can only work with the inputs and parameters you set it up with.
nosjwshere 8y ago
reverse engineering is cheaper
coldtea 8y ago
"Relatively simply structures" can be nigh impossible to model... https://en.wikipedia.org/wiki/Three-body_problem https://en.wikipedia.org/wiki/Three-body_problem

cmurf 8y ago

They aren't just good at flying. They're good at traveling on shoes, and releasing on hikes, finding their way in national forests and wilderness where they'd otherwise have had zero chance ending up.

im3w1l 8y ago

If you find this interesting I highly recommend you to look at some vape-trick videos. Smoke/steam is great at visualizing vortices, and it's absolutely astonishing how much aerodynamically control some people can achieve. Creating lots of small vortices in rapid succession, merging vortices, splitting vortices, letting vortices "suck in" other vortices. https://www.youtube.com/watch?v=Tmv228G8R4o&time_continue=1m https://www.youtube.com/watch?v=Tmv228G8R4o&time_continue=1m

hasahmed 8y ago
I feel like I could have enjoyed that if those dudes weren't such giant fuck boys
- dang 8y ago
  Please don't do this here.

seandavidfisher 8y ago

> Previous studies have found that dandelion seeds always have between 90 and 110 bristles, says Nakayama Those poor research assistants. Imagine counting hundreds of dandelion bristles every day. Probably still not possible with AI/image recognition either.

deleted 8y ago
[deleted]
nl 8y ago
That would 100% be possible with image recognition. Segment using UNet, then measure the remaining joined pixels. (Well thanks for the downvotes. I do this as my job, so I guess I'm doing the impossible or something)
- mdda 8y ago
  Perhaps people are wondering how your UNet is going to see the bristles on the other side of the dandelion seed.
  - comex 8y ago
    Take photos from multiple angles?
    - TeMPOraL 8y ago
      Now you have a pretty ugly correspondence problem to solve.
      - titzer 8y ago
        I'm glad we have experts who can count to 100 instead. /s
    - kabacha 8y ago
      And how do you deduplicate the ones that are visible on multiple angles?

a012 8y ago

I always thought dandelion seeds are like small parachutes those are slowly falling down.

mar77i 8y ago

Oh look, a vortex ring. Hermann von Helmholtz, while studying fluid dynamics predicted that vortex rings had to exist. https://www.youtube.com/watch?v=Bcr9-93wXng https://www.youtube.com/watch?v=Bcr9-93wXng

jhabdas 8y ago

Webpage not available The webpage at https://www.nature.com/articles/d41586-018-07084-8 https://www.nature.com/articles/d41586-018-07084-8 could not be loaded because: net::ERR_TOO_MANY_REDIRECTS